1. Field of the Invention
The present invention relates to a camera system for a single-lens reflex camera having an interchangeable lens, and more precisely it relates to a compatible camera system having an automatic focusing function, automatic exposure function and electrically driven power zoom function.
2. Description of Related Art
A single-lens reflex camera usually has an interchangeable lens, and accordingly, it is necessary to provide means for transmitting data peculiar to the lens, such as an open F-number (minimum F-number) which is used for an automatic exposure function and an automatic focusing function to a camera body in which the necessary arithmetic operations are effected.
To this end, a conventional photographic lens has a lens ROM which stores information peculiar to the photographic lens. A group of electrical contacts are provided, both on the camera body and on the photographic lens, so that when the lens is mounted to the camera body, as disclosed for example, in Japanese Unexamined Patent Publication No. 63-184719, which is co-pending as U.S. Ser. No. 266,328 and filed by the same assignee as the present application the lens is electrically connected to the camera body. The entire disclosure of the co-pending U.S. patent application Ser. Nos. 266,328 and U.S. Ser. No. 143,900 are expressly incorporated by reference herein.
In a conventional single-lens reflex camera, data necessary for the arithmetic operations are transmitted only in one direction, i.e. from the photographic lens to the camera body, so that based on the data, the focusing operations, actuation of the diaphragm and change of the focal length, etc. are effected by a driving power which is supplied from the camera body.
Recent motor technique developments make it possible to provide a compact and small motor as a driving source on the photographic lens without increasing the size of the lens as a whole.
A single-lens reflex camera is usually intended to be used with different photographic lenses having different steady information (fixed information), so that when the number of parameters to be controlled increases, a control unit provided in the camera body needs progressively increased arithmetic capability, resulting in an increased burden on the camera body.
Accordingly, it is preferable that the individual photographic lenses possess data processing capability for the various functions of the photographic lenses.
An advantage of the present invention is that a new camera system (camera body or photographic lens) is compatible with a conventional camera system (photographic lens or camera body).